Compressors of the free-piston resonant type driven by an electrodynamic linear oscillating motor are described in U.S. Pat. No. 3,937,600--issued Feb. 10, 1976 for a "Controlled Stroke Electrodynamic Linear Compressor" and in U.S. Pat. No. 4,067,667--issued Jan. 10, 1978 for a "Controlled Stroke Electrodynamic Oscillating Motor Compressor"--by Harlan V. White and are assigned to Mechanical Technology, Incorporated. In free-resonant piston compressors of the type disclosed in these prior art patents, the springmass system of the compressor is forced into vibration by the linear reciprocating motor and is arranged to have a selectively variable resonant frequency generally centered on the power line frequency. For this purpose the resonant piston compressor (RPC) is provided with porting means which are operative to variably control the pressure of gas in enclosed volumes which comprise resilient gas springs operative at opposite ends of each cycle of the oscillating (reciprocating) resonant piston plunger assembly. By varying the pressure of gas in the enclosed volumes comprising the resilient gas springs, the stiffness of the gas springs can be changed to thereby vary the natural frequency of the spring-mass system of the compressor. In copending U.S. application Ser. No. 160,429, filed concurrently with this application, entitled "Resonant Piston Compressor Having Improved Stroke Control for Load-Following Electric Heat Pumps and the Like", by Peter W. Curwen and Richard A. Dorman, inventors, and assigned to Mechanical Technology, Incorporated, an improved method and piston and stroke control system for an RPC is described. In this improved RPC and stroke control system, the enclosed volumes comprising the resilient gas spring means of the RPC communicate through a suitable porting system with a common manifold whose gas pressure directly controls the pressure of the gas in the enclosed volumes comprising the resilient gas spring means. The RPC of this system requires for its operation that the stiffness of the two enclosed volumes comprising the gas springs at opposite ends of the stroke of the resonant-free piston plunger assembly be controlled in order to set the resonant frequency at which the RPC operates. The stiffness of the gas springs is determined by the pressure of the gas in the enclosed volumes comprising the gas springs which in turn is controlled by the pressure of the gas in the common manifold. The present invention was devised to make available a reliable and relatively low cost gas pressure regulator valve for finely regulating (modulating) the pressure of the gas in the common manifold so as to in effect regulate the pressure of the gas in the enclosed volumes comprising the resilient gas spring means of the RPC.